Method And Tool For Closed Die Forging

ABSTRACT

A press tool for closed die forging a blank into a product is described. Said tool including upper and lower centre members and first and second side members. Said members define a cavity with the form of the product. In a two-step closed die forge process the blank is placed between said upper and lower centre members. The first and second side members are forced against the blank horizontally upsetting the outer edges of the blank. Then, the centre members are forced vertically into the blank, until the material in the blank has substantially filled the cavity.

FIELD OF THE INVENTION

The present invention relates to closed die forging in general and inparticular the forging of wheel suspension safety elements in aluminium,for the automobile industry.

TECHNICAL BACKGROUND

The common method for closed die forging aluminium is inherited fromclassical steel forging. Two dies are mounted in a press, and arepressed vertically against each other impressing their form on a blankthat lies there between. Each die includes a negative half imprint ofthe form of the finished product milled into the die material; thedimension of the imprint being corrected for the temperature of theblank and die tool. A brake surface is milled along the rim of each halfform. When the die tools are pressed against each other to the endposition, these brake surfaces form a gap or gutter of minimum 3 mm. Theforge process is “kneading” the material, and properly executed it willprovide a high strength aluminium alloy with very high endurancestrength. Thus, forging is particularly suited for highly stressedcomponents, e.g. in the wheel suspension of a car.

The classical forging process has four main drawbacks:

1. Comparatively large consumption of materials (much waste). Thepressure build up in order to fill the tool form is created by brakingthe material in the gutter. The gutter is integrated into the die tool,and follows the movement of the dies. Thus, initially the gutter forms avery large gap. The large gap will allow an easy flow of materialthrough the gutter. Only at the end of the press stroke sufficientpressure is created to fill the form. Waste of 30% is considered a verygood result (weight of waste material compared with the weight of thefinished product).

2. The press force requirements are large. At the end of the pressstroke, a large total working area (the surface of the product inaddition to the area of the gutters) must be put under sufficientpressure to get the material flowing out of the gap between the dies.

3. Requirements for special lubrication fluids, in relatively largevolumes. The material is squeezed from the centre of the tool and outthrough the brake gap/gutter with a steadily increasing pressure. Thereare large horizontal movements of material along the tool surfaces,which must be lubricated with special lubricating fluids in relativelylarge quantities.

4. The demanding requirements for centring the blank. A prerequisite forthe process is that the material should flow freely in all directions.Thus, it is not possible to place stoppers/orienting pins in the tool.The blank must therefore be placed accurately in the press, e.g. with arobot.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and toolfor closed die forging with less waste of raw materials compared withprior art methods.

Another object is to provide a method and tool for closed die forgingwhich requires less press force.

Still another object is to provide a closed die forging method and toolin which large horizontal flow of material is avoided, thus making therequirements on lubrication less stringent.

Yet still another object is to provide a method and tool for closed dieforging in which the blank is more or less self centring in the press.

These objects are achieved in a method and tool according to theappended patent claims. In particular the method includes closed dieforging a product from a preform blank of a forgeable material byplacing the blank in a press tool, said press tool including a number ofcentre and side members surrounding the blank, closing the press toolupon the blank, and forging the blank with short horizontal and verticalmovements of the tool avoiding large horizontal movements in thematerial.

The tool for forging a blank into a product according to the method inclaim 1 includes a number of upper (21) and lower (22) centre members,and first (23, 24) and second (25, 26) side members, said first (23, 24)and second (25, 26) side members enclosing said upper (21) and lower(22) centre members defining a closed cavity with the form of product.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail in reference to theappended drawings, in which

FIG. 1 is an illustration of a classical forge process according toprior art, shown in four subsequent steps,

FIG. 2 is an illustration of the inventive forge process, shown in threeindividual steps,

FIG. 3A-C shows details of the inventive forge process,

FIG. 4 shows a detail of the corresponding process of forging componentsof large width,

FIG. 5 shows typical cross sections of components manufactured with thenew process and the prior art process.

DETAILED DESCRIPTION OF THE INVENTION

The classical prior art forging process is illustrated in FIG. 1. In thefirst step, FIG. 1A, a preform blank is placed between the dies of apress. When force is applied, FIG. 1B, the material in the blank willstart to fill the form of the dies. Some material will flow horizontallyout of the die tool. FIG. 1C shows how this process continues as the dietool closes. At the end of the press stroke, FIG. 1D, the material ofthe blank fills the die form completely, with a rim of superfluousmaterial protruding out of the gutter. In a subsequent step, this rim isremoved. The amount of material that must be removed, can be equal tothe weight of the finished article, i.e. 50% of the material in thepreform blank is wasted.

In the new, inventive forge process, illustrated in FIG. 2A-C, aredesigned forge tool is used. The tool includes an upper 21 and lower22 centre member, and first 23, 24 and second 25, 26 side members. Eachside member consists of an upper part 23, 25 and a lower part 24, 26.The side members are equipped with a sloping outer surface. Two pressmembers 27 and 28 having mating sloping surfaces are acting on the sidemembers. When moving the press members vertically, their movement istranslated into a corresponding horizontal movement of the side members.In the horizontal plane, the forms of the inner surface of each sidemember will closely follow the forms of the upper and lower centremembers. Thus, when the side members are brought completely together,the tool will form a closed unit. The whole assembly rests on a table29.

Initially, the blank 20 is placed between the centre members 21, 22clamping the blank in position. Then, the side members 23, 24 and 25, 26are closed upon the blank. By this arrangement, it is not necessary toplace the blank with great precision, as the tool itself will align theblank in a correct position when the side members close upon it.

In the first forge step, FIG. 2B, the press members 27, 28 are forceddownwards until they butt against the table 29. This results in ahorizontal movement of the side members, which will upset the ends ofthe blank. The side members will close against the centre members. Thematerial in the blank is pressed horizontally from the ends into the dieform, which will become about ⅔ filled.

Synchronously, or when the horizontal movement is finished, the centremembers are forced together squeezing until the material has filled therest of the form. This step is illustrated in FIG. 2C. Due to the smallwidth of the centre members, a relatively small press force is requiredcompared with the prior art forge method.

In this embodiment of the inventive forge process, a small fixed brakegap may be employed, in the range of 0.5-1.0 mm. The brake gap is mainlyincluded in order to allow the form to be filled completely, whiletaking care of small differences in the volume of the blank. The amountof waste material is negligible. However, an additional step is neededfor removing the rim of waste material.

In the embodiment shown in FIG. 3 A-C, the brake gap is dispensed withaltogether. The figures show only a detail of the tool.

In FIG. 3A, the tool has just been closed. The side member includes nogutter, and is shaped like a blunt wedge. When force is applied thisblunt wedge will engage the blank; the blank will become upset at therim and start filling the cavity in a proper way, as illustrated in FIG.3B. In FIG. 3B the horizontal movements have been completed. Thematerial in the blank has been upset at the rim, and now partially fillsthe cavity formed by the side members. By using side member of thisparticular shape, one is assured that the blank is upset at the correctplace. Else, the upsetting action could start at any point along theblank, e.g. in the middle, preventing the material filling the cavity asit should.

In FIG. 3C also the vertical movements have been completed. The materialfrom the blank now nearly completely fills the cavity. Only smallinterstices remain. Tolerances as to the volume of the blank will betaken care of by these voids.

In case the width of the product exceeds about 30 mm, the centre membersmust be divided into several sub-members, as illustrated in FIG. 4.Thus, the central part of the product will form ribs or a honeycombpattern in order to achieve sufficient “kneading” without largehorizontal movements of material during the second step of the forgingprocess. The figure shows a detail of the finished product.

In FIG. 5 is shown typical sections from a broad component forgedaccording to the classical method (right; rim of waste materialremoved), and according to the new inventive method (left).

1. A method for closed die forging a product from a preform blank of aforgeable material, characterized in placing the blank in a press tool,said press tool including a number of centre and side memberssurrounding the blank, closing the press tool upon the blank, byvertically clamping the blank between an upper and lower centre member,horizontally moving first and second side members synchronously towardssaid centre members centring the blank in the press tool, upsetting theouter parts of said blank with the first and second said members in acontinuation of said horizontal movement, forcing the upper and lowercentre members into the blank until the material of the blank fills acavity defined by said centre and side members, by which the blank isforged with short horizontal and vertical movements of the tool avoidinglarge horizontal movements in the material.
 2. (canceled)
 3. (canceled)4. A tool for forging a blank into a product with the method claimed inclaim 1, wherein the tool includes a number of upper and lower centremembers, and first and second side members, said first and second sidemembers enclosing said upper and lower centre members defining a closedcavity with the form of product, said first and second side membersbeing adapted to upset outer parts of the blank in short horizontalmovements, the upper and lower centre members being adapted to be forcedinto the blank causing it to fill said closed cavity.
 5. A tool asclaimed in claim 4, wherein first and second side members having slopingouter surfaces, a number of press members with mating inner surfacesacting on said first and second side members in order to force saidfirst and second side members together.
 6. A tool as claimed in claim 5,wherein first and second side members comprising upper and lower parts.7. A tool as claimed in claim 4, wherein first and second side membersincluding brake surfaces forming a gutter.
 8. (canceled)